Characterization of two polyclonal peptide antibodies that recognize the carboxy terminus of angiotensin II AT1A and AT1B receptors

Critical period for dopaminergic neuroprotection by hormonal replacement in menopausal rats

The neuroprotective effects of menopausal hormonal therapy in Parkinson's disease have not yet been clarified, and it is not known whether there is a critical period. Estrogen induced significant protection against 6-hydroxydopamine-induced dopaminergic degeneration when administered immediately or 6 weeks, but not 20 weeks after ovariectomy. In the substantia nigra, ovariectomy induced a decrease in levels of estrogen receptor-α and increased angiotensin activity, NADPH-oxidase activity, and expression of neuroinflammatory markers, which were regulated by estrogen administered immediately or 6 weeks but not 20 weeks after ovariectomy. Interestingly, treatment with angiotensin receptor antagonists after the critical period induced a significant level of neuroprotection. In cultures, treatment with 1-methyl-4-phenylpyridinium induced an increase in astrocyte-derived angiotensinogen and dopaminergic neuron death, which were inhibited by estrogen receptor α agonists. In microglial cells, estrogen receptor β agonists inhibited the angiotensin-induced increase in inflammatory markers. The results suggest that there is a critical period for the neuroprotective effect of estrogen against dopaminergic cell death, and local estrogen receptor α and renin-angiotensin system play a major role.

Novel role of mechanosensitive AT1B receptors in myogenic vasoconstriction

Myogenic vasoconstriction is an inherent property of vascular smooth muscle cells (VSMCs) of resistance arteries harboring ill-defined mechanosensing and mechanotransducing elements. G protein-coupled receptors (GPCRs) are discussed as mechanosensors in VSMCs. In this study, we sought to identify and characterize the role and impact of GPCRs on myogenic vasoconstriction. Thus, we analyzed mRNA expression levels of GPCRs in resistance versus preceding conduit arteries revealing a significant enrichment of several GPCRs in resistance vessels. Selective pharmacological blockade of the highly expressed GPCRs in isolated murine mesenteric arteries ex vivo decreased myogenic vasoconstriction. In particular, candesartan and losartan most prominently suppressed myogenic tone, suggesting that AT1 receptors play a central role in myogenic vasoconstriction. Analyzing angiotensinogen(-/-) mice, a relevant contribution of locally produced angiotensin II to myogenic tone could be excluded. Investigation of AT1A (-/-) and AT1B (-/-) murine mesenteric arteries revealed that AT1B, but not AT1A, receptors are key components of myogenic regulation. This notion was supported by examining fura-2-loaded isolated AT1A (-/-) and AT1B (-/-) VSMCs. Our results indicate that in VSMCs, AT1B receptors are more mechanosensitive than AT1A receptors even at comparable receptor expression levels. Furthermore, we demonstrate that the mechanosensitivity of GPCRs is agonist-independent and positively correlates with receptor expression levels.

Lack of specificity of commercial antibodies leads to misidentification of angiotensin type 1 receptor protein

The angiotensin II type 1 receptor (AT(1)R) mediates most hypertensive actions of angiotensin II. To understand the molecular regulation of the AT(1)R in normal physiology and pathophysiology, methods for sensitive and specific detection of AT(1)R protein are required. Here, we examined the specificity of a panel of putative AT(1)R antibodies that are commonly used by investigators in the field. For these studies, we carried out Western blotting and immunohistochemistry with kidney tissue from wild-type mice and genetically modified mice lacking the major murine AT(1)R isoform, AT(1A) (AT(1A)KO), or with combined deficiency of both the AT(1A) and AT(1B) isoforms (AT(1AB)KO). For the 3 antibodies tested, Western blots of protein homogenates from wild-type kidneys yielded distinct bands with the expected size range for AT(1)R. In addition, these bands appeared identical in samples from mice lacking 1 or both murine AT(1)R isoforms. Additionally, the pattern of immunohistochemical staining in kidneys, liver, and adrenal glands of wild-type mice was very similar to that of AT(1AB)KO mice completely lacking all AT(1)R. We verified the absence of AT(1)R subtypes in each mouse line by the following: (1) quantitative polymerase chain reaction documenting the absence of mRNA species, and (2) functionally by assessing angiotensin II-dependent vasoconstriction, which was substantially blunted in both AT(1A)KOs and AT(1AB)KOs. Finally, these antibodies failed to detect epitope-tagged AT(1A)R protein overexpressed in human embryonic kidney cells. We conclude that anti-AT(1)R antibodies available from commercial sources and commonly used in published studies exhibit nonspecific binding in mouse tissue that may lead to erroneous results.

Modulation of angiotensin II and norepinephrine-induced plasminogen activator inhibitor-1 expression by AT1a receptor deficiency

Angiotensin (Ang) II stimulates plasminogen activator inhibitor-1 (PAI-1) expression in many cell types by mechanisms that are cell-type specific. We measured effects of Ang II or norepinephrine on PAI-1 expression in wild type (WT) and Ang type-1a receptor knockout mice (AT(1a)-/-) in the presence or absence of the non-specific AT(1) antagonist losartan. Ang II and norepinephrine increased systolic blood pressure equally, whereas losartan decreased the pressor response of the former but not the latter in WT mice. In AT(1a)-/- mice, baseline systolic blood pressure was lower with no effect of Ang II, norepinephrine, or losartan. Ang II stimulated PAI-1 expression in the heart, aorta, and kidney and markedly in the liver of WT mice. In AT(1a)-/- mice, Ang II-stimulated PAI-1 was significantly attenuated compared with the WT in the heart and aorta but significantly enhanced in the kidney. Losartan decreased the induction in the aorta and liver of WT, and in the kidney and liver of AT(1a)-/- mice. Norepinephrine increased PAI-1 expression in WT heart and aorta, and in AT(1a)-/- heart, kidney, and liver with no effect of losartan. Renal PAI-1 expression correlated with AT(1b) receptor mRNA. We conclude that Ang II stimulates PAI-1 expression in part through the AT(1b) receptor in the kidney and liver. Further, norepinephrine induces PAI-1 expression in vivo with AT(1a) receptor deficiency modulating the effect.